My 1992 GMC Sierra ext. cab p/u has an a/c problem. When it is first started for the day (in the morning), it blows very cold air. I have a 14 mile drive to work and it stays cool the entire trip.
At lunch, the a/c stays cool for about 3-4 minutes, then it starts to get warm and gets a musty smell. If I accelerate heavily, the cool air starts to come back, but when I let off the accelerator, the air gets warm again. It kind of jumps back and forth between cool and warm and will eventually go completely warm. If I turn off the a/c for about 10 minutes, it is cool again but only for a while.
About two years ago I replaced the pressure switch (?) that is by the evaporater (?) next to the firewall. I am not a mechanic so I'm not sure my terminology is correct. The "evaporater" is what looks like an aluminum can. The switch connects to the side of this can.
I did notice before the warm air thing started that the compressor seemed to be cycling on and off pretty frequently. It would kick on for about 2-3 seconds, then go off for about 5-6 seconds. BTW, this is an R12 system. I have a friend who works for an auto parts store who has access to the necessary equipment to convert it to R134 if we have to. Does anyone know if this can be done without replacing a bunch of a/c parts?
It has been this was all season (since May). It is now in the upper
90's and we will soon be over 100 when August rolls around. I would like to get this figured out before it gets outrageously hot.Thanks.